Foam supply systems of the above-indicated type are known in the art by the term CAFS (Compressed Air Foam System) and WEPS (Water Expansion Pumping System). A typical system includes a foam injector system, a water pumping system, and an air system including an air compressor for supplying air under pressure. For example, when employing mixture ratios of 1 CFM of air to 1 GPM of water, these systems can produce very desirable results in fire fighting by the use of "Class A" or "Class B" foams to help achieve fire suppression and to deal with increased fire loads and related hazards.
With the present day systems of the indicated type it is difficult under fire fighting conditions to maintain the water pressure and the air pressure at desired levels. At a fire fighting scene, unless an operator is present at all times to observe the flow conditions and is skilled at operating the equipment to make the necessary adjustments thereof, it is possible for the system to run out of water, to run out of foam, to lose prime in the water pump, to mix air with water by itself without the foam concentrate, to put air into the system by itself, and to even overpressurize the air. The occurrence of any of the above events, in addition to the occurrence of other possible problems, can be hazardous to the firefighter.
Various types of foam fire extinguishing systems are known, such as the valve-controlled systems disclosed in the references cited in application Ser. No. 07/955,322, now U.S. Pat. No. 5,255,747. However, these systems do not disclose control means in accordance with the present invention to automatically maintain the air flow delivered by the compressor at a desired relation to the water flow delivered by the water pump.